1. Field of the Disclosure
This application relates to a system for activating and deactivating bipolar electrodes and more particularly relates to a circuit for automatically activating and deactivating an electrosurgical generator based on tissue impedance.
2. Background of Related Art
Electrosurgery is the application of high frequency electrical current to a surgical site for tissue cutting and/or coagulation. In monopolar electrosurgery, a source or active electrode delivers radio frequency energy from the electrosurgical generator to the tissue and a return electrode carries the current back to the generator. In monopolar electrosurgery, the source electrode is typically part of the surgical instrument held by the surgeon and applied to the tissue to be treated. A patient return electrode is placed remote from the active electrode to carry the current back to the generator.
In bipolar electrosurgery, one of the electrodes of the hand-held instrument functions as the active electrode and the other as the return electrode. The return electrode is placed in close proximity to the active (current supplying) electrode such that an electrical circuit is formed between the two electrodes. In this manner, the applied electrical current is limited to the body tissue positioned between the electrodes. When the electrodes are sufficiently separated from one another, the electrical circuit is open and thus inadvertent contact of body tissue with either of the separated electrodes does not cause current to flow. The advantages of bipolar electrosurgery over monopolar electrosurgery include 1) use of lower power level which translates to less tissue destruction, 2) reduced danger of alternate site burns since the only tissue destroyed is that located between the bipolar electrodes; and 3) lower applied voltage which decreases the chance of tissue charring and scarring due to sparks at the electrodes.
Typically, the surgeon activates the electrosurgical generator by a hand or a foot switch to apply current to the body tissue. Such manual operation can cause the surgeon to inadvertently move the bipolar instrument from the desired surgical site as the surgeon activates the switch. Sometimes, to avoid excessive and unwanted surgeon body movement and consequent displacement of the instrument, the surgeon will rely on nurses or other operating room personnel to activate and deactivate the generator. This can cause unintended power delivery or undesired duration of power delivery if not properly coordinated with the surgeon. Also, due to the limits of human reaction time or machine response time when hand or foot activated switches are utilized, repeated desiccation of tissue at consistent levels can sometimes be difficult.
In U.S. Pat. No. 5,514,129, an attempt is made to automatically key the generator to avoid the drawbacks sometimes associated with and hand and foot switches. This keying and control are based on tissue impedance measurements. If the tissue impedance lies within a preset range, the generator is turned on and if the impedance falls below a preset level or exceeds a preset level, the generator is turned off. Patient tissue impedance is measured between the bipolar electrodes by measuring the instantaneous voltage variation and the instantaneous current variation between the electrodes. A first calculator divides the voltage and current proportional signals to generate a signal representative of short circuit impedances. A second calculator divides the voltage and current proportional signals to obtain the changes in impedance between the electrodes. A first comparator compares the signals from the first calculator against a first reference to identify short conditions between the bipolar electrodes and a second comparator compares the signals from the second calculator against a second reference to identify changes in impedance. A logic analyzer electrically connected to the comparators controls the generator by starting, operating and stopping the generator based on the evaluations of the signals from the comparators. The circuit of the '129 patent therefore monitors the voltage and the current and uses those values to calculate the instantaneous impedance, thus requiring the additional steps of repeated calculations to determine the impedance before assessing the impedance ranges. In order to make these measurements of voltage and current variations, RF current must be delivered to the patient.
U.S. Pat. No. 4,416,277 discloses a monopolar system utilizing impedance measurements to mandate termination of power once the generator is already activated and current is being delivered. More specifically, the '277 patent discloses a return electrode monitoring system having patient impedance detection circuitry for producing a voltage which is a function of the impedance between the split electrodes of the return electrode. The voltage signal is applied to adaptive threshold circuitry to determine if the impedance is within a desired range. If the range is exceeded, a signal is generated to disable the generator of the monopolar system.
It would be beneficial to provide a system that automatically activates and deactivates an electrosurgical generator in a bipolar system. The present disclosure provides such a system that utilizes tissue impedance measurements in a bipolar system to not only turn the generator off if the impedance value is exceeded, but to key the generator as well. This automatic activation and deactivation of the generator overcomes the disadvantages associated with manual switches. The circuitry of the present disclosure also simplifies, in part by speeding up the calculations, the activation and deactivation functions.